(a) Field of the Invention
The present invention relates to a device having an efficient heat radiation casing and, more particularly, to a device having an efficient radiation casing of a closed structure, for use as a communication device in a base station of a portable telephone system.
(b) Description of the Related Art
Telecommunication devices for use in base stations of a portable telephone system have been remarkably reduced in their dimensions, resulting from the recent development of the semiconductor technology. Accordingly, the amount of heat generated per unit area inside the communication device is significantly increased, which requires an efficient heat radiation from the device. On the other hand, the number of closed type telecommunication devices including waterproofing has increased because these devices are installed outside more and more frequently with the reduction of the dimensions.
Referring to FIG. 1 showing a conventional communication device mounted on a pole 12 with a pair of straps 13, the communication device 30 has a casing 31 with a radiator 32 mounted on the back surface thereof. Referring additionally to FIG. 2 showing a partial sectional view of the communication device of FIG. 1, taken along a horizontal plane, the radiator 32 is attached to the casing 31 for radiating the heat generated in a heat source 26 toward outside the casing 31. A gasket 33 is inserted between the casing 31 and the outer periphery of the radiator 32 for assuring a waterproof function.
The radiator 32 is generally made by machining a drawn aluminum bar, which raises the cost of the device. The natural radiation of the device through the radiator 32 and the casing 31 requires a large external surface area of the device, which raises the external dimensions and the weight of the device. In particular, the radiation efficiency depends on the wind velocity around the device, wherein a small wind velocity reduces the radiation efficiency.
The radiator 32 has a plurality of grooves for air flow, which limits the allowable posture of the casing 31 so that the grooves of the radiator 32 extend in the vertical direction.
Referring to FIG. 3 showing a sectional view of another conventional communication device, the communication device has a casing 41 separated by a heat insulator plate 42 into two chambers 43 and 44. The chamber 44 receives therein a main power circuit 52 which radiates a large amount of heat, whereas the chamber 43 receives therein a control circuit 51 such as a printed circuit board, which radiates a smaller amount of heat and is less heat-resistant compared to the main power circuit 52. A fan 53 is installed in the chamber 44, with a radiator 54 such as a fin attached to a portion of the casing 41 for the chamber 44. The communication device of FIG. 3 is described in JP-A-4-32300.
The proposed device, however, requires a large external surface area for heat radiation, and the fan 53 and the radiator 54 increase the dimensions of the communication device. In addition, the control circuit 51 is significantly affected by the heat generated in the main power circuit 52 notwithstanding the improved structure.